An international bird flu expert says despite two Vietnamese patients dying after developing a tamiflu resistant strain of bird flu, most patients respond to the drug.
Professor Arnold Monto, from the University of Michigan, said it was expected that the bird flu virus H5N1 would evolve into resistant forms.
The deaths were reported this week in the New England Journal of Medicine.
But Prof Monto said the fact the two Vietnamese patients had developed the resistant strain may not have in itself caused their deaths.
"I think that really has very little to do with the outcome, namely that both of them died, especially since one of them was actually treated six days into the illness," Prof Monto told National Radio.
"The virus has developed resistance. We knew that this was going to happen.
"But we also know, for example, that a girl treated with tamiflu some months ago (had) resistant virus but yet recovered," he said.
"So I don't know if the resistance is what is producing the bad effect in both of these cases, or the fact that treatment didn't start early enough in most cases, and if it was started early perhaps the disease was too far gone in order for the drug to work."
Dr Mark Jacobs, director of public health, said it could not be known for sure whether tamiflu would cure people sick with the bird flu virus.
But New Zealand had followed the advice of the WHO (World Health Organisation) to stockpile anti-viral medicines to prepare for a pandemic, he said.
The ministry would continue to monitor international developments, including whether there may be a need in the future to add to the anti-viral stockpile, he said.
Prof Monto said while it was expected that the virus would develop some resistance, it was not expected to develop to a level where when a patient became infected with the virus they would be resistant from the start.
Countries around the world have scrambled to stockpile tamiflu to counter a global-pandemic.
New Zealand's Health Ministry has spent $26 million storing 850,000 doses of Tamiflu, which is roughly enough to treat 21 per cent of the population.
Prof Monto said tamiflu had been selected over the alternative anti-viral drug relenza.
"We have selected tamiflu because it is absorbed and disseminated in the body. Relenza is an alternative, and there is an IV or intravenous preparation that might be used if resistance is encountered," he said.
- NZPA WGT hl kk